What’s the significance of unleavened bread in Exodus 12? Is it a time-saver because it had to be eaten in haste? Did leaven represent the corruption of sin and therefore was to be avoided by God’s people?

Here is a comment from Philip Ross:

[L]eaven was a lump of dough kept over from the previous day that would be added to the next batch of dough causing the bread to rise. … God’s command, ‘Observe the feast of Unleavened Bread for on this very day I brought you out of the land of Egypt’ (Exod. 12:17), suggests that the unleavened bread was to be a repeated reminder that at the Passover they had broken their links with Egypt and were to live in marked discontinuity with its ways…

– From the Finger of God, p.293.

Unleavened bread: a reminder of redeeming grace.